Power tools such as sanders, grinders and polishers are usually equipped with a spindle lock to prevent rotation of the output spindle while mounting or removing the wheels or discs. The lock pin is designed so it can be engaged only when the spindle is stopped or rotating substantially below operating speed. Engagement at operational speeds is prevented by having the hole engaged by the pin only slightly larger than the pin so the pin cannot be aligned with and pushed into the hole at high speed . . . there just is not enough time. When the pin is engaged only 1 or 2 degrees of spindle rotation is possible. The torque required to remove a disc or wheel generally requires use of a wrench and restraint of the tool to take up the reaction--all while holding the lock pin engaged.
If the pin engaged in a substantially larger "hole", the spindle could then be manually rotated to impact on the pin and facilitate removal (mounting) of the accessory without wrenches or having to restrain the tool. But the pin would then enter the hole at operational speeds with serious damage to the tool.